This invention relates to improvements in log charger systems for veneer lathes. More particularly the invention relates to improvements in such charger systems having automated scanning equipment for sensing the shape of a log and positioning the log for optimum production of veneer.
In the design of veneer production equipment, the primary objectives are to maximize the yield of usable veneer from the irregularly-shaped logs from which the veneer is peeled, and to maximize the production rate of the veneer. In order to attain these objectives great effort has been expended in the development of sophisticated, automated log scanning equipment, primarily of the electro-optical type, for sensing the shape of each log and rapidly determining its longitudinal axis for optimum veneer production. Examples of such scanning systems used or usable for this purpose are contained in the following U.S. Pat. Nos. 3,736,968; 3,746,065; 3,787,700; 3,852,579; 3,890,509; 3,902,539; 3,992,615; 4,197,888; and 4,221,973. Electro-optical scanners constructed in accordance with the foregoing technology, and particularly those which rotate the log during the scanning process, are extremely accurate and have the capability of determining the location of the log axis for optimum veneer production to within a few thousandths of an inch.
While such a high degree of accuracy in determining the optimum peeling axis should theoretically maximize the yield of veneer from each log, the results obtainable in practice have unfortunately fallen short of this goal because the mechanical log manipulators of veneer lathe chargers are incapable of duplicating the scanner's degree of accuracy. Thus, although the scanning system may identify the location of the optimum peeling axis of a log to within a few thousandths of an inch, the mechanical log manipulators responsible for aligning such axis with the rotational axis of the lathe actually allow a much wider margin for error than that tolerated by the scanning system. Because of this discrepancy in tolerances between the electro-optical and mechanical portions of veneer lathe chargers, substantial mispositioning of the logs and less than optimum yields persist despite the provision of the highly accurate scanning systems.
The progress of log manipulating mechanisms, as opposed to scanning systems, in veneer lathe chargers is exemplified by U.S. Pat. Nos. 3,037,538, 3,664,395, 3,746,065, 3,752,201, 4,197,888 and 4,246,940. In general, all of such chargers attempt to hold the log at either a prepositioning or a scanning station to determine its optimum peeling axis, adjust the position of the log such that the optimum axis is aligned with a reference axis, and transfer the log to the veneer lathe such that the optimum axis is aligned with the rotational axis of the lathe. In these few mechanical steps, however, there are many opportunities for log positioning errors. Relatively large errors can occur, for example, if at any point from the initiation of prepositioning or scanning to the securing of the log in the lathe, the log is supported by engagement with its curved surface at points intermediate its ends, rather than by end engagement. The error problem is further compounded when rotary scanning is not used and the optimum axis is therefore determined from insufficient information regarding the log's profile.
In addition to mechanical inaccuracy, the speed of log manipulation by veneer lathe chargers has been hampered by unnecessary time lags between log manipulating steps, thereby adversely affecting production rate.